Infectious diseases do not respect boundaries, and a pandemic is by definition an epidemic infectious disease that spreads rapidly to several areas of the world, although evidence shows that new outbreaks usually start in Asia or Africa. Most new pandemics have originated through the “zoonotic” transmission of pathogens from animals to humans. Zoonoses from domesticated animals are concentrated in areas with intensive and extensive farming and livestock production systems and live animal markets.
Dense concentrations of population, especially in urban centers, can act as focal points for disease transmission and accelerate the spread of pathogens. Moreover, social inequality, poverty, malnutrition, and calorie deficits weaken an individual’s immune system, while environmental factors such as lack of clean water and adequate sanitation amplify transmission rates and increase morbidity and mortality. An unprecedented shift in human population with rapid urbanization is one reason why more diseases originate in Asia and Africa, where 60% of the world already lives. Migration on that scale means forest land is destroyed to create residential areas. Wild animals, forced to move closer to cities and towns, inevitably encounter domestic animals and the human population. Wild animals often harbor viruses; bats, for instance, can carry hundreds of them. Viruses, jumping from species to species, can ultimately infect people. Eventually, extreme urbanization becomes a vicious cycle: more people bring more deforestation, and human expansion and the loss of habitat ultimately kills predators, including those that feed off rodents responsible of zoonotic disease.
On both of these continents (meaning Asia and Africa) many families depend on farming and a minuscule supply of livestock. Disease control, feed supplementation and housing for those animals is extremely limited.
